The seatbelt portion of a vehicle restraint system secures the occupant of a vehicle against harmful movement that may result from a vehicle collision. The seatbelt functions to reduce the likelihood of injury by reducing the force of occupant impacts with vehicle interior structures. In this role the seatbelt applies loads across the chest or lap of the occupant. Controlling or reducing these loads may reduce the risk of occupant injury during a collision. A seatbelt system may include a retractor that incorporates a load limiting device. The retractor includes a spool around which the webbing is wrapped. In the event of a vehicle impact, the spool is locked, preventing its rotation and preventing unwinding of the webbing. A load limiting mechanism within the retractor allows control or reduction of restraint load transmitted to the occupant during a vehicle impact. A known load limiting mechanism includes a torsion bar disposed in a center of the spool. The torsion bar may be a cylindrical bar of steel having a yield strength selected to allow the bar to torsionally yield at a predetermined value limiting the loads transmitted to the occupant, thus reducing risk of injury during a vehicle impact. Twisting of the torsion bar absorbs some of the inertia energy, thereby reducing the load sustained by the occupant against the webbing. The torsion bar, when plastically deformed, may yield in a non-linear manner that may be difficult to duplicate. It is desired to provide an improved load limiting mechanism.